Naturally acquired immunity (NAI) to high-density parasitemia and clinical illness from P. falciparum (Pf) and P. vivax (Pv) infection develops slowly during childhood and wanes in the absence of periodic boosting from blood stage infection. Serum IgG antibodies are critical for development of this acquired immunity. The slow acquisition of NAI arises, in part, from an impaired ability to generate persisting malaria-specifi memory B cells (MBC) and resulting long-lived Ab secreting plasma cells (LLPC) to a broad repertoire malaria Ags. Blood stage Pf and Pv may suppress generation and maintenance of malaria MBC and LLPC by virtue of their high Ag loads that elicit systemic pro-inflammatory responses, e.g. increased TNF-, IFN-y which are eventually down-regulated (possibly explaining, in part, why many malaria infected children in endemic areas are asymptomatic). In the current proposal, we examine the hypothesis that the inflammatory milieu elicited by repeated malaria infections among individuals with little or no NAI, e.g. young children and malaria nave adults, upregulates potent inhibitory feedback loops that impair generation and maintenance of MBC and LLPC. A central goal of research here is to establish a link between susceptibility to malaria infection and uncomplicated morbidity and the ability to generate and sustain malaria Ag-specific MBC. We will evaluate and compare these relationships with respect Pf and Pv since NAI to Pv develops more rapidly than to Pf under conditions of similar transmission in Papua New Guinea (PNG). The studies will be performed with collaborators from West Africa and NIH in order to determine whether these features of NAI are generalized across populations that diverge genetically and epidemiologically. While immune regulatory mechanisms will be considered broadly using gene microarray analysis of known or suspected feedback loops, inhibitory Fc?RIIB that regulates the B cell receptor (BCR) activation threshold by binding malaria Ag immune complexes (IC) will be evaluated specifically. We will use biological samples and clinical/parasite data from children and adults exposed to Pv and Pf in PNG under the auspices of approved IRB protocols of the SW Pacific ICEMR. The specific objective of the project are: i) Correlate the degree of NAI with malaria Ag-specific MBC frequency, breadth and durability; ii) Determine the immunoregulatory networks elicited by acute malaria and their relation to generation Pf MBC; (iii) Assess whether FCGR2B functional polymorphisms impact NAI and malaria Ag-specific MBC development.